1. Field of the Invention
The present invention generally relates to a mechanism for regulating back pressure of a scroll compressor. More particularly, the present invention relates to a mechanism for automatically regulating back pressure of a fixed scroll of a scroll compressor.
2. Background of the Invention
Scroll compressors have been widely employed in air conditioners. An example of the scroll compressors is shown in Taiwan Patent Publication No. 263024. FIG. 1 of the attached drawings shows a conventional scroll compressor. The conventional scroll compressor comprises a pair of scrolls, respectively called fixed scroll 10 and rotating scroll 11. The fixed scroll 10 is in general fixed and thus not rotatable, while the rotating scroll 11 is rotatable with respect to the fixed scroll 10. The rotation of the rotating scroll 11 drives working fluid, such as coolant, from a low pressure chamber 12 located on the back side of the rotating scroll 11 to a high pressure chamber 13 located on the back side of the fixed scroll 10 and thus compressing the working fluid.
Also referring to FIG. 7 which shows plots of the back pressure and scroll separation force of a scroll compressor vs. pressure difference between the high pressure chamber 13 and the low pressure chamber 12. In FIG. 7, Curve A represents the scroll separation force occurring during the operation of the scroll compressor. The term xe2x80x9cscroll separation forcexe2x80x9d as used herein indicates the force caused by the compressed working fluid acting between and thus tending to separate the fixed scroll 10 and the rotating scroll 11. This may lead to leakage of the compressed working fluid between the scrolls 10.
The scroll separation force changes in accordance with the operation conditions of the compressor. An example of the operation conditions of the scroll compressor that affects the scroll separation force is the pressure difference xcex94P between the high pressure chamber 13 and the lower pressure chamber 12 of the scroll compressor. During the operation of the scroll compressor, it is common to make use of the pressure difference between the high pressure chamber 13 and the low pressure chamber 12, serving as a back pressure acting upon the fixed scroll 10, to overcome the scroll separation force and thus eliminating leakage of working fluid between the scrolls 10, 11 caused by the separation of the scrolls 10, 11.
In the conventional design of the scroll compressor shown in FIG. 1, forces caused by the pressure difference xcex94P act upon a boss 100 and a plurality of back pressure carrying pins 14 to provide the desired back pressure for retaining the fixed scroll 10 in position.
Curve B of FIG. 7 shows the distribution of the back pressure employed in the conventional design. In the conventional design, only a single point of the back pressure curve is taken into consideration. Namely, the design is based on a xe2x80x9cfixedxe2x80x9d back pressure. The fixed point is usually the most frequently occurring back pressure of the scroll compressor, such as pressure difference xcex94P2 of FIG. 7. The design is done by adding a desired margin to the corresponding scroll separation force. This is the back pressure desired to overcome the separation force and keep the scrolls 10, 11 together. The back pressure is the sum of the forces acting upon the boss 100 and the pins 14 and it is in general equal to the sum of the scroll separation force plus the safety margin. The overall surface area of the boss 100 and the pins 14 can thus be determined which in turn determines the slope of Curve B.
The conventional design is particularly suitable for scroll compressors that operate under fixed pressure difference. By suitably selecting the overall surface area of the boss 100 and the pins 14, a sufficient back pressure may thus be obtained to overcome the scroll separation force. However, when a scroll compressor does not work in a fixed pressure difference condition, such as the condensation temperature and the evaporation temperature changing with the surroundings, the conventional design suffers the following disadvantages:
(1) When the scroll compressor is operating in a low pressure difference zone, namely the difference between the condensation temperature and the evaporation temperature is small, such as the zone between zero pressure difference and xcex94P2 of FIG. 7, the back pressure (Curve B) is close to the scroll separation force (Curve A) causing an insufficiency of back pressure. Satisfactory sealing between the scrolls may not be kept and leakage of working fluid occurs.
(2) When the scroll compressor is operating in a high pressure difference zone, namely the difference between the condensation temperature and the evaporation temperature is large, such as the zone between xcex94P2 and xcex94P3 of FIG. 7, the situation is reversed. With the increase of the pressure difference, the back pressure acting on the fixed scroll 10 via the boss 100 and the pins 14 is increased and may significantly exceeds the desired back pressure thereby leading to undesired friction and thus wearing between the scrolls 10, 11 and between the rotating scroll 11 and the support frame 15. Damage of the parts and waste of electrical power that is used to drive the rotating scroll 11 may thus be caused.
Increasing the overall surface area of the boss 100 and the pins 14 results in a steep slope of Curve B. This, although helping solving the insufficient back pressure problem encountered in a low pressure difference operation condition, excessively increases the back pressure in the high pressure difference operation condition, resulting in reduction of the service life of the parts. Thus, there always needs a compromise between the leakage problem caused by insufficient back pressure and the wearing problem caused by excessive back pressure.
It is thus desirable to have a back pressure regulation mechanism for overcoming the above mentioned problems.
Accordingly, an object of the present invention is to provide a back pressure regulation mechanism for a scroll compressor which help maintaining a suitable back pressure for all operation conditions. In other words, when the scroll compressor is operating in a low pressure difference condition, the back pressure regulation mechanism provides a sufficient back pressure to the fixed scroll in order to avoid leakage of the compressed working fluid. On the other hand, when the scroll compressor is operating in a high pressure difference condition, the back pressure regulation mechanism limits the back pressure applied to the fixed scroll to a desired value so as to avoid excessive back pressure acting upon the fixed scroll and thus alleviating wearing occurring on the parts of the compressor.
In accordance with the present invention, the back pressure regulation mechanism comprises a plurality of back pressure regulation devices engaging with the fixed scroll and a boss extending from the fixed scroll. The back pressure regulation devices provide a force acting on the fixed scroll, the force being proportional to the pressure difference during the operation in a low pressure difference zone, while being constant during the operation in a high pressure difference zone. Thus when scroll compressor is operating in the low pressure difference zone, the force provided by the back pressure regulation device, plus a force provided by the boss, both resulting from the pressure difference, is sufficient to compensate the scroll separation force and thus eliminating leakage problem and when the scroll compressor is operating in a high pressure difference zone, the constant force provided by the back pressure regulation devices limit the increased amount of the force acting upon the fixed scroll and thus alleviating the excessive back pressure problem.
An illustrative example of the back pressure regulation device in accordance with the present invention comprises a back pressure carrying pin movably received in a bore and a resilient energy storing element, such as a disk spring is arranged between the pin and the fixed scroll for transmission of the force from the pin to the fixed scroll. The movement of the pin is limited by upper and lower limit positions whereby in the low pressure difference zone, the pin does not reach the lower limit position and the force transmitted to the fixed scroll by the disk spring is proportional to the pressure difference, while in the high pressure difference zone, the pin reaches and is stopped at the lower limit position, the force transmitted to the fixed scroll is thus maintained constant, not changing with the pressure difference.